I would like to upload .ai, psd., .eps, and similar formats, but somehow when I tried to upload ai. and .eps files I get the error message: invalid type file. How could i solve that? my server's mime types includes application/postscript: ai, eps, ps and my OC's server settings includes those ones as allowed file extensions. so what could be the issue?

When we upload through upload+ it only allows the "Allowed Files". I think you need to change the allowed files in manager upload. You can check the list of allowed files in settings->DefaultCart->Edit>under options tab. Maybe change the code in the admin->controller->common->filemanger.php. Or you can use a module to upload